The earth has gotten greener…

- NASA satellites observed greening during the 21st century
- populous and developing countries
- regions far removed from human reach
- Svalbard, in the high-arctic, 30% ↑ greenness
- concurrent with ↑ in summer temperature from 2.9 to 4.7C
- What is the role of plants in global change?
- question is a matter of scale
Leaf area index: What it means to be greener


Why are plants producing more leaf area?

- Humans dump ~40 billion tons of CO2 into atmosphere
- Atmospheric CO2 is a greenhouse gas
- ↑ CO2 = ↑ trapped heat = ↑ surface temperatures
- Plants fix CO2 from the atmosphere via Rubisco
Greenhouse gases make the earth warm

A carbon imbalance exists between surfaces and air

Plants represent a large carbon sink

The role of vegetation change

- Ability to immediately fix carbon from atmosphere
- photosynthesis - respiration
- keeping pace with human emissions?
- Sequestrating carbon in wood
- prevents fast cycling of carbon
- Transpiration adds H2O into atmosphere
Plant carbon uptake is multi-layered

Vegetation change is not new!


Global plant C sink: Photosynthesis


Just plant tons of trees, problem solved…

- Are all trees carbon vacuums?
- fast growing trees don’t live as long
- fast growing trees drain more water
- fast growing trees create less dense wood
- Farmland to forests: can we eat?
- Are all forests equal?
- forest plantation = rain forest?
How sustainable is the CO2 fertilization effect


Global plant C sink: Nutrient limitation


Global plant C sink: Climate warming


Global plant C sink: Climate warming

- Plants like higher temperatures to a degree
- faster rate of photosynthesis (limited)
- most plants not operating at Topt
- Rubisco cheats more at high temperatures
- Dependent on stomatal behavior
- Warming may also mean ↓ precipitation
Global plant C sink: Respiration

Climate change is altering precipation regimes


Key questions: How plastic are plants?
- Phenotypic plasticity: allows individuals to respond to change within their lifetime
- acclimation (lifetime) vs adaptation (generations)
- Can plants change physiology to match new conditions?
- can optimums be adjusted?
- Why might northern species struggle in warmer temperatures?
- Why might plants struggle in new precipitation regime

Climate changes are just part of global change
- Lots of other stresses on plant communities
- impact sustainability of greening earth
- Habit degradation from human activities
- Total habitat loss
- agricultural conversion
- urban growth
- Higher rates of exotic species invasions

Is the earth still getting greener?
- Greening since 1980’s reduced warming ~0.2C
- New science suggests browning trend
- greening trend stalling or reversing
- Related to less moisture in the air
- higher VPD from climate warming
- Why would drier air impact plant growth negatively…
- Plant carbon sink does not fix global carbon imbalance
